SOHC.co.uk Forums > CB350/400
No Vacuum on Carb#1
element137:
sounds like a similar bit of kit to what I have used for the sync - I did think that the adapter on Carb 1 might be dodgy so swapped it for another one from the kit and no different - on carbs 2/3/4 they worked a treat and they were pretty close from bench sync to start with - just Carb#1 gauge not registering any vacuum -
Rob62:
Sounds a bit worrying, if there is no vacuum that means there is insufficient movement or air through the cylinder which could be damaged, bent or burned out valves or missing, broken or stuck rings or a holed piston.... you should be able to get an early indication of the situation by putting your thumb over the plug hole and turning the motor over.
element137:
Update : Cylinder 1 compression OK - and getting a spark - turns out the lack of vacuum on CYL 1 when using 4 bank carb sync gauges = blocked adapter :-[ - last week I only tested the gauge by sucking on the tube - swapped the adapter over and got vacuum on cylinder 1 OK - so down to cheap crap vac gauge set - lesson learned - combination of cheap gauge and my dumbness -
Had it running this morning - idle is a bit erratic with a bit of surging - but now CYL 2 intermittent not firing - pulled the plug - and intermittent spark/weak yellow - any ideas on this ? coils ? - if I remember the coil on 2 is paired with 3 ? which is running OK - its running what looks like a very old Piranha electronic ignition -
Bryanj:
New plug caps, trim the ends of the HT leads and try again
element137:
Thank you Bryanj - I followed your bench sync process ( thank you very much for that ) - as I mentioned in prev post its running very rich, starts without choke, and the idle screw is screwed so far out that its no longer in contact with the bar - I am just about to pull the carbs off again as the idle is rough/surging (as well as the spark issue on CYL2) - in your opinion - with the idle screw in this position ( ie, redundant ) , is it possible i have screwed up the carb rebuild please ? apologies if its a bit of a how long is piece of string question - I don't really want to take the carbs apart again if I can help it - but I am sort of convinced something not right ? - could the over rich issue be the air / mix screw ? - currently set all four at 1.5 turns out and untouched at this point -appreciate any thoughts
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